Thanks for testing this and for all the replies, guys. Animating symbol instances rather than the symbol itself makes quite a difference.
GreenSock does not render animated SVG symbols properly in Chrome (44.0.2403.155.m) and IE 11.0.21 on Windows 7 SP1 x64. Please have a look at the Codepen example. The animations render properly in Firefox 40.0.2. There is no animated scale in IE and nothing is animated in Chrome.